Thermostat



C. E. ARMSTRONG THERMOSTA'I' Filed June 10, 1957 Aug. 16, 1 960 CHARLES E. ARMSTRONG INVENTOR.

United States Patent THERMOSTAT Charles E. Armstrong, Portland, Oreg., assignor to C. E. Armstrong Company, Gladstone, 0reg., a corporation of Oregon Filed June 10, 1957, Ser. No. 664,565

2 Claims. (Cl. 200-138) This invention rel-ates to improvements in temperature sensitive thermostats of the type generally known as line voltage direct load thermostats particularly adapted for use in electrically heated homes and the like. Thermostats of this character generally have a 20 ampere, 250 volt rating and are intended to be capable of controlling temperature at one degree or less temperature differential.

It is one of the principal objects of my invention to provide a thermostat of the character described which will operate on less than one-half of one degree temperature diiferential. To achieve this object I utilize the combination of a bi-metal temperature sensitive element and a snap acting switch which has the distinct characteristic of operating on an extremely close movement differential of less than one one-thousandth of an inch and on a pressure differential of approximately three ounces.

In order to achieve sufficient bi-metal to operate the switch on such small differential and at the same time render the thermostat as small and compact as possible, I provide two short strips of bi-metal arranged in parallel spaced relation to each other with one of the strips in contact with the actuating plunger of the switch for actuating the same. The arrangement is such that deflection in -both strips is combined in concentrated reaction against the switch actuating plunger. The other bi-metal strip which is not in direct contact with the switch plunger is under considerably less strain and therefore can be of less thickness and thereby capable of greater deflection for a given temperature change than the plunger-contacting strip. This greater deflection of the thin strip is transmitted into thefree end of the thicker strip which functions as a lever to thereby concentrate the combined pressure force of both strips of bi-metal at the switch plunger.

A further object of the invention is the incorporation therein of the feat-ure of heat anticipation. This I accomplish by a simple yet novel arrangement of electrical conductors into the housing of the thermostat and relative to the bi-metal strips therein so that the latter will partake of and react to the inherent heat of the conductors caused by the flow of current through the conductors. It is well known that amperage passing through an electrical conductor will cause a slight rise in ambient temperature and this I utilize to give the thermostat the necessary boost which heretofore was obtained by connecting a resistor into the line which added to the cost of producing the thermostat and to its installation.

The foregoing and other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawing forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

Figure 1 is a front view of a thermostat made in accordance with my invention and with a fragment of its housing broken away for convenience of illustration.

Figure 2 is a sectional side view of Figure l with the housing removed and showing a sectional fragment of an electrical outlet box to which the thermostat is attached and thereby supported upon a wall.

Figure 3 is a rear view of Figure 1 with the housing removed.

Figure 4 is a view similar to Figure 2 showing a modified formof the invention.

With continuing reference to the drawing, reference numeral 1 indicates a base frame capable of mounting by means of fastening screws 2 to an electrical outlet box 3 secured to a wall or other supporting surface in the conventional manner. A chassis 4 is secured to the base frame by hooked engagement as at 5 at one of its ends and by fastening screws 6 at the other. The chassis is formed with a central opening 7 and opposing parallel flanges 8 along the sides thereof. The flanges are apertured for the reception of fastening screws 11 by means of which a micro switch 12 is secured between the flanges and also bearing plates 13 are secured to the flanges. The plates 13 are apertured to receive hinge pins 15 and 16 to which are hingedly attached respectively an inner temperature sensitive element 17 and an outer temperature sensitive element 18. Both elements are of the bi-metal type and the element 18 is preferably .030" in thickness while the element 17 is .040. One end of the element 18 is at all times in contact with the corresponding end of the element 17 either by means of a screw 19 or said ends could he turned into abutting engagement if desired. The opposite end of element 18 is in adjustable contact by means of an adjusting screw 20 with the cam-face 21 of a temperature-selecting dial 22 pivotally attached as at 23 to one end of the chassis 4.

The micro switch 12 is provided with the usual actuating plunger 24 whose outer end, as best shown in Figure 2, is at all times in contact with the temperature sensitive element 17 as shown. Upon a rise in temperature the bi-metal strips 17 and 18 will deflect outwardly relative to each other as indicated by broken lines. The greater deflection of the thinner strip 18, as aforesaid, for a given temperature change is transmitted into the free end of the strip 17 which strip then functions as a lever against the switch plunger 24 under the combined press-ure force of both strips 17 and 18. Hence it will be apparent that the switch will be operated on an extremely close movement differential and under maximum pressure.

In the modification shown in Figure 4 17A indicates a non-temperature sensitive lever hingedly attached as at 15A at one of its ends to the bearing plate 13A and in contact with the switch plunger 24A intermediate its ends. The free end of the lever 17A is in contact at all times with the free end of a bi-metal strip 18A hingedly attached as at 16A to the bearing plate 13A and in adjustable contact as at 20A at its opposite end with the temperatureselecting dial 22A. In operation the bi-metal strip 18A will deflect as indicated by broken lines and in so doing apply pressure to the outer or free end of the lever 17 whereby, as in the other form of the invention, the switchplunger 24A will be depressed by the power arm of the lever.

The electrical conductors to the switch are indicated at 26 and 27 and to accomplish the heat-anticipation feature the invention. Having thus described my invention what I claim as new and desire to protect by Letters Patent is:

1. A thermostat of the class described comprising in combination a base, a switching mechanism carried by the base and connected into a load circuit by electrical conductors extending into and looped within the base, a switching mechanism carried by the base, a first temperature sensitive element hingedly attached at one of its ends to the base and intermediate its ends in operative contact with the switching mechanism, a second temperature sensitive element hingedly attached intermediate its ends to the base and in contact at one of its ends with an adjustable cam surface upon the base and at its opposite end in contact with the opposite end of the first temperature sensitive element, whereby the deflection of both temperature sensitive elements is combined in concentrated reaction against the switching mechanism to actuate the same, and said electrical conductors within the area of said base being so arranged relative to said temperature sensitive elements that the latter will partake of and react to the inherent heat of said conductors caused by the flow of current therethrough.

2. A thermostat as in claim 1 wherein each of said temperature sensitive elements is of bimetal comprising .4 a high and a low expanding side, the low expanding side of one temperature sensitive element opposing the low expanding side of the other whereby the deflection of both temperature sensitive elements on a rise or fall of temperature will result in their deflection in opposite directions from one another, and whereby the deflection of one temperature sensitive element is transmitted into the other and their combined deflection is directed against said switching mechanism.

References Cited in the file of this patent UNITED STATES PATENTS 1,506,769 Newell Sept. 2, 1924 2,217,488 Mahnke Oct. 8, 1940 2,279,929 Schournaker Aug. 14, 1942 2,306,810 Jones Dec. 29, 1942 2,383,414 Osterheld Aug. 21, 1945 2,704,841 Van Ryan Mar. 22, 1955 2,733,315 Richardson Jan. 31, 1956 2,803,786 Edsall Aug. 20, 1957 FOREIGN PATENTS 742,724 Great Britain Jan. 4, 1956 

